1. Field of the Invention
This invention relates to a membrane type artificial lung and to a method for the manufacture thereof. More particularly, this invention relates to a membrane type artificial lung for removing carbon dioxide gas from blood and adding oxygen to blood during the course of extra-corporeal blood circulation. The artificial lung of the present invention exhibits biocompatibility, an insignificant loss of platelets, and excellent gas-exchange ability, and provide a method for the manufacture thereof.
2. Description of the Prior Art
Heretofore, as an auxiliary means for a cardiotomy, an artificial lung which is adapted to effect exchange of gases by exposing the blood in circulation to an oxygen-containing gas through the medium of a gas exchange membrane possessed of a satisfactory permeability to gas has been known. The gas-exchange membranes which are used in membrane type artificial lungs of the above described class are of two types, homogeneous membranes and porous membranes.
As homogeneous membranes, silicone membranes are currently used. However, since silicone membranes are used, the homogeneous membranes do not have sufficient strength for the membranes to be produced in a thickness below 100 .mu.m. The membranes consequently have limited permeability to gas and exhibit particularly poor permeability to carbon dioxide gas. When some tens of thousands of hollow fiber membranes are bundled for the purpose of attaining a desired gas-exchange ability, the apparatus designed to operate with this bundle of membranes occupies a large volume, requires a large amount of priming, and proves very costly.
The porous membranes known in the art are made of various materials such as, for example, polyethylene, polypropylene, polytetrafluoroethylene, polysulfones, polyacrylonitrile, polyurethane, and polyamides. These gas-exchange membranes are required to possess large permeability coefficients with respect to O.sub.2 and CO.sub.2, refrain from inducing leakage of blood plasma during protracted circulation of blood, and avoid inflicting upon the blood damage due to physical contact as in the coagulation of blood, formation of microthrombosis, loss of platelets, degeneration of blood plasma proteins, and hemolysis. None of the gas-exchange membranes developed so far satisfies all these requirements. Particularly in terms of damage to blood or biocompatibility, even, silicone membranes which are rated as superior to all of the other membranes are still not satisfactory. In the extracorporeal circulation of blood such as in the use of an artificial lung, it has been customary to perform a chemotherapy for suppressing thrombosis by the addition of heparin simultaneously, for example. It has been found, however, that while the heparin can be expected to be effective in suppressing coagulation, it has virtually no effect upon the agglutination and aggregation of platelets.
The porous membranes literally possess numerous minute pores running throughout in the direction of wall thickness. Since the membranes are hydrophobic, they permit the addition of oxygen from the feed gas to blood and the removal of carbon dioxide gas from blood into the gas without the passage of blood plasma through the minute pores, i.e. leakage of blood plasma from the blood path side of the membrane to the gas path side thereof. Owing to their high permeability to steam, however, the porous membranes not only exhibit degradation of performance by dew, but also induce leakage of blood plasma during protracted service in circulation of blood. This adverse phenomenon is witnessed even in the case of those porous membranes which have successfully passed the water leakage test performed during the course of manufacture of an artificial lung.
With the goal towards eliminating the various drawbacks of the conventional porous membranes as described above, we have proposed an artificial lung using porous membranes having the minute pores thereof blocked with silicone oil (Japanese Patent Application SHO 58(1983)92,325) and a further improved artificial lung using porous membranes having the minute pores thereof blocked with silicone rubber (Japanese Patent Application SHO 59(1984)105,384). The artificial lung which uses porous membranes having the minute pores thereof blocked with silicone rubber no longer encounter the problem of blood plasma leakage which is observed in the artificial lungs using the conventional porous membranes. It nevertheless does not have the sufficient ability to remove carbon dioxide gas. As a result, it has experienced difficulties in removing the amount of carbon dioxide gas produced in the living body with such a low flow volume of blood as in the extracorporeal circulation such as, for example, the ECCO.sub.2 R (extracorporeal CO.sub.2 removal).
An object of this invention, therefore, is to provide a novel membrane type artificial lung and a method for the manufacture thereof.
Another object of this invention is to provide a membrane type artificial lung adapted to remove carbon dioxide gas from blood and add oxygen to the blood during the course of the extracorporeal circulation of blood. The artificial lung of the present invention has a greater ability to remove carbon dioxide gas and has no possibility of inducing leakage of blood plasma during a protracted use and a method for the manufacture thereof.
A further object of this invention is to provide a membrane type artificial lung which is most suitable for ECCO.sub.2 R and a method for the manufacture thereof.